Academic journal article Environmental Health Perspectives

Chemical Characterization and Bioactivity of Polycyclic Aromatic Hydrocarbons from Non-Oxidative Thermal Treatment of Pyrene-Contaminated Soil at 250-1,000 [Degrees] C

Academic journal article Environmental Health Perspectives

Chemical Characterization and Bioactivity of Polycyclic Aromatic Hydrocarbons from Non-Oxidative Thermal Treatment of Pyrene-Contaminated Soil at 250-1,000 [Degrees] C

Article excerpt

In this paper we report yields, identities, and mutagenicities of products from heating a polycyclic aromatic hydrocarbon (PAH)-contaminated, Superfund-related synthetic soil matrix without exogenous oxygen. We heated batch samples of soil pretreated with 5.08 wt% (by weight) pyrene in a tubular furnace under a constant flow of helium gas at 250, 500, 750, and 1,000 [+ or -] 20 [degrees] C. Dichloromethane (DCM) extracts of cooled residues of heated soil and of volatiles condensed on a cold finger after 1 sec residence time at furnace temperature were assayed gravimetrically and analyzed for PAH by HPLC, HPLC coupled to mass spectrometry, and gas chromatography coupled to mass spectrometry. All four temperatures volatilized pyrene and generated other PAHs, including alkylated pyrenes. We detected bioactive PAHs in the product volatiles: cyclopenta[cd]pyrene (CPP) at 750 and 1,000 [degrees] C and benzo[a]pyrene (BaP) at 1,000 [degrees] C. We found a clean soil residue, i.e., no pyrene or other DCM extracts, only at 750 [degrees] C. Control experiments with uncontaminated soil, pyrene, and Ottawa sand plus 4.89 wt% pyrene revealed no CPP or BaP production from soil itself, but these experiments imply that pyrene interactions with soil, e.g., soil-bound silica, stimulate CPP and BaP production. We detected mutagenicity to human diploid lymphoblasts (in vitro) in volatiles from 1,000 [degrees] C heating of soil plus pyrene and sand plus pyrene, and in the residue from 500 [degrees] C heating of soil plus pyrene. Three plausible pathways for pyrene conversion to other PAHs are a) a reaction with light gas species, e.g., soil- or pyrene-derived acetylene; b) loss of [C.sub.2]-units followed by reaction with a PAH; and c) dimerization with further molecular weight growth via cyclodehydrogenation. This study shows that thermal treatment of PAH-polluted soil may generate toxic by-products that require further cleanup by oxidation or other measures. Key words: benzo[a]pyrene, cyclopenta[cd]pyrene, decontamination, mutagenicity, PAHs, polycyclic aromatic hydrocarbons, pyrene, soil, thermal. Environ Health Perspect 108:709-717 (2000). [Online 23 June 2000]

http://ehpnet1.niehs.nih.gov/docs/2000/108p709-717richter/abstract.html

Contaminated soil harms the environment when natural or human forces transfer its pollutants to other venues, e.g., surface or subsurface aquifers and the ambient atmosphere. Efficient cleanup of contaminated soils without hazardous by-products is thus a major goal of environmental remediation initiatives such as the U.S. Superfund Basic Research Program (1). Thermal decontamination technologies are of significant scientific and practical interest because they can provide high destruction and removal efficiencies for organic pollutants (2), and they have often been selected for cleanup of Superfund sites (2,3). Further, new methods for above-ground and in situ treatment may innovate and extend the applicability of soil thermal cleaning technologies. Broadly based public acceptance is essential to siting and operating environmental technology in the United States. For soil thermal remediation, a notable concern is that process residues or effluents may jeopardize human health (4), for example, because of inadequate cleaning of targeted pollutants or generation of hazardous by-products (5) during routine or off-specification operations. Detailed scientific and engineering understanding of soil thermal treatment is useful in the design, operation, monitoring, and innovation of remediation technologies and should thus be of interest to diverse stakeholders.

Laboratory scale research has mimicked thermal and chemical environments of practical processes to elucidate underlying details of soil thermal decontamination, for example, see Saito et al. (6). One technique ohmically heated (~1,000 [degrees] C/sec) captive samples of powdered soil supported on a thin metal foil (7-9). Bucala et al. …

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